vinyl: do not create empty runs
vinyl: do not create empty runs

Currently, we create a run file and add a new run to the list even if
it's empty and therefore there's no point in keeping it. Besides being
pointless, this feature also stands in the way of multilevel compaction,
where dumped runs are supposed to define the size of the first level of
the LSM tree. If a run is empty, the math behind the level size
computation does not work and should be special-cased, which look ugly.
That said, let's just drop empty runs right away.

rtsisyk/tarantool,rtsisyk/tarantool,mejedi/tarantool,mejedi/tarantool,rtsisyk/tarantool,mejedi/tarantool,rtsisyk/tarantool,mejedi/tarantool